Utilising Apache server to block IP addresses should reduce the load on php and/or mySql servers. As this plugin will eliminate the need to process HTTP requests and then matching the referrer IP address with blacklist stored on mySql.

This plugin can also integrate with Wordfence Security (if installed) to import blocked IPs from Wordfence and also block IPs on Wordfence.

How to use:

Install the plugin and activate it.

Go to Control Panel of the plugin and make sure to follow the instructions exactly. The instructions are tailored to your site.